Williams translates Viejas and Viejos as “old women's voice” and
“old men's voice”, and describes them as regals
with “stopped resonators of similar length for all pitches” and thin,
nasal tone.
Grove describes them as thin
Vox humanas
in Spanish organs around 1750, often found en chamade.
Maclean describes Viejos and Viegas as the bass
and treble portions, respectively, of an 8' Vox Humana.
Wedgwood translates Viejos as “the eyebrows”, and says:
“The stop is said to derive its name from the shape of the cover
or plug at the top of the pipe. (Hamilton's ‘Catechism of the Organ’).”

The following photographs are of the
Jorge Bosch Bernat-Veri organ at the Royal Palace, Madrid, Spain,
and appear here courtesy of Rick Berg.

The pipes to either side of the console are the
Viejos/Viejas.
Right above them are the pipes of the Orlos, and above that, the
Trompetería.